Class MessageFormat

MessageFormat provides a means to produce concatenated
messages in a language-neutral way. Use this to construct messages
displayed for end users.

MessageFormat takes a set of objects, formats them, then
inserts the formatted strings into the pattern at the appropriate places.

Note:MessageFormat differs from the other Format
classes in that you create a MessageFormat object with one
of its constructors (not with a getInstance style factory
method). The factory methods aren't necessary because MessageFormat
itself doesn't implement locale specific behavior. Any locale specific
behavior is defined by the pattern that you provide as well as the
subformats used for inserted arguments.

Within a String, a pair of single quotes can be used to
quote any arbitrary characters except single quotes. For example,
pattern string "'{0}'" represents string
"{0}", not a FormatElement. A single quote itself
must be represented by doubled single quotes '' throughout a
String. For example, pattern string "'{''}'" is
interpreted as a sequence of '{ (start of quoting and a
left curly brace), '' (a single quote), and
}' (a right curly brace and end of quoting),
not'{' and '}' (quoted left and
right curly braces): representing string "{'}",
not"{}".

A SubformatPattern is interpreted by its corresponding
subformat, and subformat-dependent pattern rules apply. For example,
pattern string "{1,number,$'#',##}"
(SubformatPattern with underline) will produce a number format
with the pound-sign quoted, with a result such as: "$#31,45". Refer to each Format subclass documentation for
details.

Any unmatched quote is treated as closed at the end of the given
pattern. For example, pattern string "'{0}" is treated as
pattern "'{0}'".

Any curly braces within an unquoted pattern must be balanced. For
example, "ab {0} de" and "ab '}' de" are
valid patterns, but "ab {0'}' de", "ab } de"
and "''{''" are not.

Warning:

The rules for using quotes within message
format patterns unfortunately have shown to be somewhat confusing.
In particular, it isn't always obvious to localizers whether single
quotes need to be doubled or not. Make sure to inform localizers about
the rules, and tell them (for example, by using comments in resource
bundle source files) which strings will be processed by MessageFormat.
Note that localizers may need to use single quotes in translated
strings where the original version doesn't have them.

The ArgumentIndex value is a non-negative integer written
using the digits '0' through '9', and represents an index into the
arguments array passed to the format methods
or the result array returned by the parse methods.

The FormatType and FormatStyle values are used to create
a Format instance for the format element. The following
table shows how the values map to Format instances. Combinations not
shown in the table are illegal. A SubformatPattern must
be a valid pattern string for the Format subclass used.

Usage Information

Here are some examples of usage.
In real internationalized programs, the message format pattern and other
static strings will, of course, be obtained from resource bundles.
Other parameters will be dynamically determined at runtime.

The first example uses the static method MessageFormat.format,
which internally creates a MessageFormat for one-time use:

Note: As we see above, the string produced
by a ChoiceFormat in MessageFormat is treated as special;
occurrences of '{' are used to indicate subformats, and cause recursion.
If you create both a MessageFormat and ChoiceFormat
programmatically (instead of using the string patterns), then be careful not to
produce a format that recurses on itself, which will cause an infinite loop.

When a single argument is parsed more than once in the string, the last match
will be the final result of the parsing. For example,

Constructor Detail

MessageFormat

Constructs a MessageFormat for the default
FORMAT locale and the
specified pattern.
The constructor first sets the locale, then parses the pattern and
creates a list of subformats for the format elements contained in it.
Patterns and their interpretation are specified in the
class description.

MessageFormat

Constructs a MessageFormat for the specified locale and
pattern.
The constructor first sets the locale, then parses the pattern and
creates a list of subformats for the format elements contained in it.
Patterns and their interpretation are specified in the
class description.

applyPattern

Sets the pattern used by this message format.
The method parses the pattern and creates a list of subformats
for the format elements contained in it.
Patterns and their interpretation are specified in the
class description.

setFormatsByArgumentIndex

Sets the formats to use for the values passed into
format methods or returned from parse
methods. The indices of elements in newFormats
correspond to the argument indices used in the previously set
pattern string.
The order of formats in newFormats thus corresponds to
the order of elements in the arguments array passed
to the format methods or the result array returned
by the parse methods.

If an argument index is used for more than one format element
in the pattern string, then the corresponding new format is used
for all such format elements. If an argument index is not used
for any format element in the pattern string, then the
corresponding new format is ignored. If fewer formats are provided
than needed, then only the formats for argument indices less
than newFormats.length are replaced.

setFormats

Sets the formats to use for the format elements in the
previously set pattern string.
The order of formats in newFormats corresponds to
the order of format elements in the pattern string.

If more formats are provided than needed by the pattern string,
the remaining ones are ignored. If fewer formats are provided
than needed, then only the first newFormats.length
formats are replaced.

Since the order of format elements in a pattern string often
changes during localization, it is generally better to use the
setFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the
order of elements in the arguments array passed to
the format methods or the result array returned by
the parse methods.

setFormatByArgumentIndex

Sets the format to use for the format elements within the
previously set pattern string that use the given argument
index.
The argument index is part of the format element definition and
represents an index into the arguments array passed
to the format methods or the result array returned
by the parse methods.

If the argument index is used for more than one format element
in the pattern string, then the new format is used for all such
format elements. If the argument index is not used for any format
element in the pattern string, then the new format is ignored.

Parameters:

argumentIndex - the argument index for which to use the new format

newFormat - the new format to use

Since:

1.4

setFormat

Sets the format to use for the format element with the given
format element index within the previously set pattern string.
The format element index is the zero-based number of the format
element counting from the start of the pattern string.

Since the order of format elements in a pattern string often
changes during localization, it is generally better to use the
setFormatByArgumentIndex
method, which accesses format elements based on the argument
index they specify.

getFormatsByArgumentIndex

Gets the formats used for the values passed into
format methods or returned from parse
methods. The indices of elements in the returned array
correspond to the argument indices used in the previously set
pattern string.
The order of formats in the returned array thus corresponds to
the order of elements in the arguments array passed
to the format methods or the result array returned
by the parse methods.

If an argument index is used for more than one format element
in the pattern string, then the format used for the last such
format element is returned in the array. If an argument index
is not used for any format element in the pattern string, then
null is returned in the array.

getFormats

Gets the formats used for the format elements in the
previously set pattern string.
The order of formats in the returned array corresponds to
the order of format elements in the pattern string.

Since the order of format elements in a pattern string often
changes during localization, it's generally better to use the
getFormatsByArgumentIndex
method, which assumes an order of formats corresponding to the
order of elements in the arguments array passed to
the format methods or the result array returned by
the parse methods.

format

Formats an array of objects and appends the MessageFormat's
pattern, with format elements replaced by the formatted objects, to the
provided StringBuffer.

The text substituted for the individual format elements is derived from
the current subformat of the format element and the
arguments element at the format element's argument index
as indicated by the first matching line of the following table. An
argument is unavailable if arguments is
null or has fewer than argumentIndex+1 elements.

formatToCharacterIterator

Formats an array of objects and inserts them into the
MessageFormat's pattern, producing an
AttributedCharacterIterator.
You can use the returned AttributedCharacterIterator
to build the resulting String, as well as to determine information
about the resulting String.

The text of the returned AttributedCharacterIterator is
the same that would be returned by

In addition, the AttributedCharacterIterator contains at
least attributes indicating where text was generated from an
argument in the arguments array. The keys of these attributes are of
type MessageFormat.Field, their values are
Integer objects indicating the index in the arguments
array of the argument from which the text was generated.

The attributes/value from the underlying Format
instances that MessageFormat uses will also be
placed in the resulting AttributedCharacterIterator.
This allows you to not only find where an argument is placed in the
resulting String, but also which fields it contains in turn.

Will not always find a match (or the correct match)
if some part of the parse is ambiguous.
For example, if the pattern "{1},{2}" is used with the
string arguments {"a,b", "c"}, it will format as "a,b,c".
When the result is parsed, it will return {"a", "b,c"}.

If a single argument is parsed more than once in the string,
then the later parse wins.

When the parse fails, use ParsePosition.getErrorIndex() to find out
where in the string the parsing failed. The returned error
index is the starting offset of the sub-patterns that the string
is comparing with. For example, if the parsing string "AAA {0} BBB"
is comparing against the pattern "AAD {0} BBB", the error index is
0. When an error occurs, the call to this method will return null.
If the source is null, return an empty array.

parseObject

The method attempts to parse text starting at the index given by
pos.
If parsing succeeds, then the index of pos is updated
to the index after the last character used (parsing does not necessarily
use all characters up to the end of the string), and the parsed
object array is returned. The updated pos can be used to
indicate the starting point for the next call to this method.
If an error occurs, then the index of pos is not
changed, the error index of pos is set to the index of
the character where the error occurred, and null is returned.